I don't believe the arcs after Whole Cake Island have added anything new to this, but there are some issues with your assumptions. This is what the wiki on Chapter 818 states about the Road Poneglyphs (emphasis mine):
The Straw Hats are astonished that this poneglyph can lead them to Laugh Tale, but Inuarashi backtracks, revealing that there are four Road Poneglyphs. He states that each poneglyph does not lead to Laugh Tale, but rather to an island surrounding it. When all four islands are found and linked, the way to Laugh Tale will be shown.
The way this is phrased, it might be important to visit all islands and perform some action there to "link" them in order to reach Laugh Tale. The One Piece world does have a lot of unusual geography and erratic weather phenomenon, so extrapolating the location might not be a valid option.
Geometrically, we know this:
Each Road Poneglyph gives a location, and the four locations create a quadrangle with Laugh Tale in the intersection of the diagonals.
While the diagonals in a parallelogram (like squares and rectangles) will definitely intersect at their midpoints, it is possible to have quadrilateral shapes where diagonals intersect at some different ratio (for example, a kite-like shape or an irregular shape).
Additionally, even if the diagonals meet at their midpoint, unless you find poneglyphs that give you two locations diagonally opposite to each other, you'd end up going to the midpoint of an edge, which is the wrong location.